Abstract

The main topic of this research is modelling and design of high-speed, large-force and long life-time electromagnetic actuators based on Magnetic Shape Memory (MSM) alloys. These relatively new “smart” alloys that change shape in magnetic fields possess very promising properties such as large strain, considerable output stress and potentially very long fatigue life. However, there is still lack of a consistent design methodology for MSM-based devices which can be implemented using techniques common for engineering design. In order to bridge this gap, a modelling approach for MSM element in actuators is developed in which the complete magnetic circuit of MSM actuator is included into a single finite element (FE) model. This approach also allows accurate representation of MSM permeability change during the shape change capturing its effects on total reluctance of the magnetic circuit. Moreover, this approach allows studying the magnetic field distribution in the MSM element in single, two and multi-variant states in magnetic fields of varying strength. The modelling results show striking non-homogeneity of the magnetic field distribution, providing new insights on the magneto-mechanical behaviour of the MSM element. The modelling approach is verified through comparing the calculated MSM permeability change with previously reported results obtained by measurement.

Using this modelling approach, electromagnetic analysis is conducted for eleven MSM actuators. The actuators are designed and optimised for a particular 0.1mm strain (displacement) and 10N force output for implementation in food-sorting machines. The conducted analysis also ensures robustness of the designs and stable multi-billion cycle operation. The very long lifetime is achieved through careful analysis of the magnetic circuit and the behaviour of the MSM element during operation.

Finally, thermal analysis is conducted for the designed actuators in order to ensure their thermal stability. In order to overcome challenges associated with a very low operating temperature limit of the MSM element in actuators, different available cooling conditions are studied. Moreover, an energy-efficient operation cycle is developed that takes advantage of the shape memory effect of the MSM element also taking into account the pressure change in the pneumatic valve of a sorting machine. The analysis shows multiple regimes which allow thermal stability in a 300Hz pulsed excitation cycle. Implementation of the developed operating cycle also leads to the considerable increase in overall efficiency.